Water Heater Guide

Unvented

Unvented systems are fed directly from the cold water mains supply; therefore no expansion tank is required.  Unvented Water Heaters can therefore offer a number of benefits compared to conventional “vented” systems including higher pressure and flow rates and balanced hot/cold supplies.  Unvented water heaters are ideal where hot water is required for multiple outlets such as kitchens or wash rooms, or larger capacities are available for more commercial options, such as dishwashing, hand washing or low demand canteen use.  Unvented Water Heaters can also offer flexible siting as there is no need for a cold water cistern.

Vented (Point of Use)

Vented Water Heaters are generally installed directly over the sink area, and are commonly referred to as “Point of Use”.  They have an open outlet and rely on the opening of a tap or valve on the inlet side to displace the hot water in the heater with the incoming cold water. The open outlet ensures that any excess pressure in the heater is vented.  Water expansion is accommodated by allowing the water to drip from the spout.

Point of use Water Heaters are ideal for use with single sink requirements, for example in kitchens, surgeries, and workshops.

Over-sink/Under-sink

Water Heaters enable more siting flexibility as they are available in models that can be either installed over-sink or under-sink, depending on your requirements.  Each over-sink or under-sink model, work in exactly the same way and offer equally good performance.  Therefore the only actual difference is where you position it.  Particularly popular is the Ariston Europrisma, a top quality Unvented Water Heater that is available in over-sink or under-sink, and offers 10 litre or 15 litre capacities. 

Water Heater Accessories

When installing Unvented Water Heaters it is important that the right accessory packs are used.  As every installation is different, accessory packs are used to ensure that the water heater is installed correctly and safely.  In some cases, expansion in a cold water main is restricted via a stop valve, check valve or water meter, and an accessory pack which includes an expansion vessel must be fitted.  It is also essential that you are aware of your maximum incoming water pressure prior to installation.

There are a variety of accessory packs available, dependant on your circumstances, and PlumbNation recommends that you seek expert advice from either your installer or manufacturer, if you are unsure of your installation requirements.